The present invention relates to a system for smoothing or spreading transitions between image regions in television signals. The signals to be transmitted are processed in a still picture signal processing method and in a motion picture signal processing method. Particularly, the present invention is a circuit for accurately detecting a motion signal which represents a moving image so as to control the transitions between image regions of a frequency-unfolded image signal.
Standard television systems such as an NTSC or a PAL system process a television signal adaptively in accordance with an amount of motion in of the signal. This adaptive processing of the signal may result in some quasi-motion picture regions between image regions being processed in a still picture signal processing method and other image regions being processed in a motion picture signal processing method. If differences in the processing methods used in different regions are perceptible to a viewer, or if the transitions between the different regions are discerned by a viewer, image quality if degraded.
As an example of such adaptive processing for the purpose of separating chrominance and luminance components from a composite video signal, a frame comb filter or a line comb filter may be used. As long as there is no change in the image signal at frame time intervals, chrominance and luminance components from the composite video signal can be completely separated, using the frame comb filter. If the scene changes over the frame time intervals, then some color information will be present in the separated luminance component, and some brightness information will be present in the chrominance component.
A line comb filter, also used to separate the luminance and chrominance components from the composite video signal, does not produce significantly degraded component signals in the presence of image motion. However, the line comb filter reduces the vertical resolution of the reproduced image more than the frame comb filter. In addition, in locations where a vertical transition occurs, an image processed by the line comb filter may be degraded due to both color information being introduced into the luminance component, producing an image artifact known as hanging dots, and brightness information being introduced into the chrominance, producing incorrect colors in the neighborhood of the transition.
Therefore, the television signal should be adaptively processed by detecting the presence or absence of image motion. In the regions in which the image is stationary, the frame comb filter is used, and in the regions in which the image is moving, the line comb filter is used.
An example of adaptive processing is an adaptive double-scanned, non-interlaced scan converter. In such a converter, interstitial lines are displayed between lines of the current field. However, the interstitial lines may be those transferred from the preceding field in the presence of image changes producing visible artifacts such as serrated contours. The interstitial lines may also be interpolated from lines within the current field, but the vertical resolution is reduced, and line flicker may occur. In regions in which image changes are detected, intrafield interpolated interstitial lines are displayed and field-delayed interstitial lines are displayed in other way.
Yet another example of such adaptive processing is adaptive peaking circuitry in which regions having relatively high noise are processed with a relatively low peaking factor and regions having relatively low noise are processed with a relatively high peaking factor.
In the above examples, the television signals are processed adaptively in response to the values of estimated parameters of the image. The parameters are motion, in the case of luminance/chrominance separation or of double scanning non-interlaced conversion, and a relative level of noise, in the case of the peaking. Differently processed regions, and noticeable boundaries between regions where the parameter is present and those where it is absent are undesirable artifacts introduced by the above types of adaptive processing types.
U.S. Pat. No. 5,113,262 issued May 12, 1992, to the inventors and others; entitled "AN IMPROVED VIDEO SIGNAL RECORDING SYSTEM" and assigned to Samsung Electronics Co., Ltd., describes a recording system for recording and reproducing a full bandwidth video signal on and from a recording medium having a limited bandwidth by folding the high frequency component of a luminance signal into the low frequency component of the luminance signal.
In U.S. Pat. No. 5,113,262 a motion signal which represents a moving image is recorded together with the folded luminance signal and the chrominance signal on the recording medium. The motion signal is used to control the transition between regions of the full bandwidth luminance signal which is unfolded into the original frequency bands during reproduction.
That is, in the previous work of the inventors and their coworkers, the high frequency component of the luminance signal is folded into the low frequency component of the luminance signal during recording. At this time, the high frequency component of the luminance signal is modulated by a folding carrier, so that the folded luminance signal has a phase difference of 180 degrees between frames, between scanning lines, and between pixels.
Accordingly, in reproducing, the high frequency component folded into the low frequency component of the folded luminance signal is demodulated by the unfolding carrier having the same phase and frequency as those of the folding carrier, so that the high frequency component of the luminance signal is unfolded into the original frequency band.
However, the folding carrier and the sideband thereof will be present in the unfolded luminance signal. The resultant luminance signal unfolded by the folding carrier and the sidebands thereof has a phase difference of 180 degrees between frames.
As a result, the conventional motion signal detecting circuit, for detecting the level difference of pixels between frames in the motion signal, has difficulty detecting accurately the motion signal from the unfolded luminance signal, due to the phase off-set between frames.
U.S. patent application Ser. No. 07/711,980 filed Jun. 7, 1991, by the inventor Ko and entitled "MOTION DETECTING CIRCUIT" corresponds to Korean patent application No. 90-18737 filed Nov. 19, 1990. These patent applications describe techniques, for eliminating the folding carrier and sidebands thereof, contained in the unfolded luminance signal by a prefilter and for detecting a motion signal through filtering, by means of a comb filter, the unfolded luminance signal in which the folding carrier and the sidebands are eliminated.
However, the above prefilter can eliminate the folding carrier and sidebands thereof contained in the unfolded luminance signal of the vertical and horizontal direction having a large correlation. But it is difficult to completely eliminate the folding carrier and sidebands thereof contained in the unfolded luminance signal in the diagonal direction, that is, the temporal direction having a small correlation.
Therefore, since the unfolded luminance signal which is output from the prefilter has a phase difference of 180 degrees from the folding carrier and sidebands remaining in the diagonal signal component, it is difficult to derive an accurate value for the diagonal direction of the motion signal, which is the difference component between flames detected by the comb filter.